The overall program of research under this Grant is designed to extend historical knowledge, and deepen our analytical comprehension of the fundamental economic forces, behavioral responses, and biological and technological conditions that governed the voluntary practice of birth control in the United States during the broad period between the 1820s and the 1930s. Our objectve is to write a quantitatively informed history of the diffusion of fertility-regulating practices during the era before highly efficient, reliable methods of contraception became available. Our research in pursuit of this goal has been structured to achieve three intermediate objectives: (1) estimation of summary statistical measures of the extent of effective marital fertility-controlling behavior among various population cohorts; (2) development of historically relevant models of life-cycle strategies of fertility regulation, and of unregulated (natural) fertility behavior; (3) analysis of the determinants of the distribution of historical populatons -- within the United States -- between strategies of non-control and control.